Okanogan, WA is supposed to get a Supercharger install sometime in 2024. That puts it in the middle of existing stations at Entiat, WA and Osoyoss, BC.
In my mind there's lots of secondary highway corridors that are devoid of Superchargers.
Theory: Tesla is concentrating their expansion of Supercharger resources to areas which have the most traffic first, dictated by the existence or feasibility of adding electrical capacity to support those Superchargers.